To support voice over Internet protocol (VoIP) over a macro network (e.g., a Long Term Evolution (LTE) network, an evolved high rate packet data (eHRPD) network, mixed LTE/eHRPD networks, etc.), enhanced emergency calls (or “E911” calls) must be supported. The macro network-based VoIP must provide a caller's (e.g., connected to the network via user equipment (UE), such as a mobile communication device, a cell phone, a mobile terminal, a smart phone, a personal digital assistant (PDA), etc.) initial and updated locations to a correct public safety answering point (PSAP). There are different ways of determining a location of a UE making an E911 call. For example, triangulation of received signals by UE from multiple cell towers (e.g., with prior knowledge of the cell tower locations) may be used to determine the location of the UE. If the UE supports global positioning system (GPS) and GPS satellite signals can be received by the UE, the GPS location of the UE can be obtained (e.g., by a network location server) by using various protocols (e.g., the open mobile alliance (OMA) secure user plane location (SUPL) protocol, the LTE location positioning protocol (LPP), etc.).
A femto cell is a small cellular base station that connects to a service provider network via broadband. A femto cell typically supports two to four mobile communication devices (e.g., UEs) in a residential setting and eight to sixteen mobile communication devices in a business setting. To support VoIP over a femto network, E911 calls must be supported as well. The femto network-based VoIP must provide a caller's (e.g., connected to the network via a UE) initial and updated locations to a correct PSAP. However, determining a position of a UE in a femto network is difficult because a femto network is typically deployed within a building where receiving a GPS signal from the UE is often impossible. Using triangulation to determine a location of a femto-based UE is often not possible either because the UE typically receives signals only from the femto cell and the femto cell's location is typically not known to a network location server. Thus, attempts to use the SUPL protocol to obtain the location of a femto-based UE will often fail.
Supporting E911 becomes even more complicated when a UE is associated with both a macro network and a femto network. For example, the UE may place the E911 call on a femto network, and the E911 call may be handed over to a macro network when the UE changes locations. Alternatively, the UE may place the E911 call on a macro network, and the E911 call may be handed over to a femto network when the UE changes locations. In both scenarios, the UE's initial location and updated location need to be known.